Screw.



No. 635,297. Patented Oct., 2.4, |899. J. W. CALDWELL.

SCREW.

(Appumon ned Lug. 1s, 189s.)

(No Model.)

Imam/ier.-

gfohn 'W Yala/well TN: Norms PETERS om Fuero-Limo., wnsulncrron. u, c.

UNTTED STATES PATENT JOHN WILLIAM CALDWELL, OF OOOLAMON, SOUTH WALES.

SCREW.

SPECIFICATION forming part of Letters Patent No. 635,297, dated October24, 1899. Application filed August I3,1898 Serial No.688,485. (Nomodel.)

To @ZZ whom, it may concern,.-

Be it known that I, JOHN WILLIAM CALD- WELL, a subject of the Queen ofGreat Britain, and a resident of Coolamon, New South Wales, andtemporarily residing in the borough of Manhattan, in the city, county,and State of New York, have invented certain new and useful Improvementsin Screws, of which the following is a specification.

This invention relates to the constructionl of threaded devices-such,for instance, as screws-and especially to that class of screws adaptedfor use in wood.

The object of the invention is to provide a threaded device or screwwhich not only has superior holding power to threaded devices or screwsas ordinarily constructed, but is otherwise more efficient than suchscrews owing to the increased rate of speed and facility with which thesame may be forced into or taken out of the wood, and this with less eX-ertion and without the choking or clogging of the threads thereof, as isthe case with ordinary screw-threads, and is also more efficient thansuch screws, since it may be readily started in ordinary wood withoutthe necessity, as heretofore, of tirstboring a hole therefor, therebyaffecting the holding power of the wood, and may also be readily driveninto place, thereby avoiding the slow and tedious operation of insertingit by means of a screwdriver.

In the drawings accompanying and forming part of this specification,Figure l is a view of one form of device, such as a wood-screw, havingthis improved construction of thread. Fig. 2 is a view of another formof such screw. Fig. 3 is a view, partly in vertical section, of a screwas ordinarily constructed. Fig. 4 is a vertical sectional view of thescrew shown in Fig. l. Fig. 5 is a vertical sectional view of the screwshown in Fig. 3. Fig. 6 is an enlarged view of the threaded portionofthis improved screw for illustrating the action of the wood iibers.Fig. 7 is a similar enlarged View of the threaded portion of a screw asordinarily constructed. Figs. 8, 9, 10, and 11 illustrate some of thedifferent forms of devices which may be provided with this improvedconstruction of threads, and Fig. 12 is an end view of the thread.

Similar characters of reference designate like parts in all the figuresof the drawings.

As a preface to a further description of this improved threaded deviceit is to be understood that while the same is shown and described hereinas a screw the invention is, nevertheless, applicable to any. kind ofdevice having threads, some forms of which are shown in Figs. 8 to ll ofthe drawings, and therefore it will be understood that by the term screwas used herein is to be understood any device having threads.

In the use of threaded devices-such, for instance, as wood-screws asordinarily constrncted-it is found in practice that they not onlyrequire considerable exertion in order to force them into the wood, butthat it takes a comparatively long time to accomplish this result owingto the necessity of first boring a hole and to theirslow speed, whichlatter is due, I apprehend, to the shape and construction of the threadsand points of the screw, which afford great resistance to thepenetration of such screw. In the screw as usually constructed since theunder beveled sides 2, Figs. 3, 5,' and 7, of the threads project orextend below the peripheral edges 3 thereof they first engage the wood,and hence form resistantsurfaces, necessitating that the wood be forcedout of the way, as at 4, Fig. 7, to permit the entrance of the screw.Moreover, owing tothe inclination of these beveled under sides 2 thewood is forced downwardly and outwardly and in a direction coincidingwith the direction the screw is working, thereby tending constantly toimpede the effective action of the screw by pressing the same outwardand by choking and clogging the threads thereof. In other words, owingto the construction of the thread in order to force the screw intoposition the wood must be displaced by a jamming or wedging action, andas the tendency of the wood fibers is to return to their normal positionthe threads are constantly being pressed outward and are choked andclogged up, whereby the free action of the screw is retarded. Inaddition to this the screw as usually constructed is provided with arelatively flat or blunt conical or beveled point 5, which isineffective to cut its way into the wood, so that to drive the IOO screwinto position considerable force is required, since the wood must beforced out of the way by a wedging action in order to permit thepenetration of the screw, during which the wood continues to impede theeffective action of the screw by its resistant pressure after the screwis entered. Furthermore, the edge of the thread being located above theunder surface thereof it has a tendency to strip the wood between thethreads, so that its drawing and holding power is eliminated, and ittherefore becomes necessary to bore a hole substantially all the way inhard wood and some distance in ordinary wood.

In the present improvement in order to avoid the defects above set forthI have provided a device in which the point and threads are soconstructed that they will act as a cutting mediuln to permit the screwto cut its way into the wood without the necessity of forcing the fibersof such wood out of the way by a wedging or jamming action, and whichthreads will also operate to clear themselves of the fibers of the wood,thereby to avoid the resistant pressure thereof, and will assist inpulling the screw into position. In a general way this improved threadeddevice embodies a thread the peripheral edge of which is so locatedrelatively to the under side of such thread that it will first engagethe wood, whereby when such edge is formed sharp the thread may act witha cutting action on the wood, thereby to permit the device to cut itsway thereinto, the upper side of such thread being so formed that itwill act to clear the threads of the fibers of the wood and so permitthe free action of the device. This improved device, furthermore,comprises a piurality of cutting points or lips, whereby the effectiveaction of the device is increased. In practice the screw may have itscore S conical throughout, Fig. 2, or it may have such core of the sameor substantially the same diameter throughout, terminating in a shortbeveled or sharp cone-shaped end 9, as desired, Fig. l.

In the construction shown the screw-core is provided with a plurality ofspiral threads shown as two in number, lO and l2, thereby forming adouble-threaded screw, the threads being preferably of a wide or openpitch, although it will be understood that any desired pitch may beused. Each of these threads I0 and 12 is so formed that its outer orperipheral edge 13 will first engage and upwardly displace the wood,thereby to decrease the resistance to the entrance of the thread, thisbeing accomplished by so forming the under side lei of the threads thatthey'do not project beyond or below the plane of such edge and which inpractice may be secured by forming the under side of such threadsrelatively flat, whereby they may be in substantially the same plane asthe peripheral edge of the threads. The peripheral edge 13 of thethread, which in practice first engages the wood, may be formed as asharp cutting edge,

whereby it will cut its way into the wood, thel under side of the threadowing,r to its formation not impeding the action of the device, so thatthe screw can be forced into the work with superior facility and withcomparatively little exertion. Since the peripheral or cutting edge ofthe screw first engages the wood or material, as hereinbefore set forth,it follows that the under surface of the thread while in the samerelative plane with the' edge and while relatively fiat, as above setforth, nevertheless must in practice be slightly above the cutting edgeof the screw, or otherwise the screw on entering the material would havethe entire under surface of its thread in engagement with the materialsimultaneously with the engagement therewith of the edge, so that inpractice the under side ofthe screw may be somewhat dipped to insure theprior engagement of the cutting edge with the wood, this also being thecase in practice with the threads located on the beveled end of thescrew of the form shown in Fig. l, since as the surfaces ot' the threadsare relatively flat and as the threads will usually have in practice thesame formation throughout the screw the under surfaces will therefore besubstantially at right angles to the surface of the core on which thethreads are carried, and as the threads on the beveled end of the screware carried on a beveled surface and are substantially at right anglesto such beveled surface they may have in practice their under surfacesso inclined or dipped as to positively insure the prior engagement oftheir cutting edges with the wood, and this throughout the length of thebeveled surface of the core. The upper sides orsurfaces 15 of thethreads are formed relatively steep, thereby forming with the relativelyfiat under sides a relatively sharp cutting edge, and owing to theserelatively steep upper sides of thev threads the tendency of suchthreads is to spring or lift the fibers of the wood upwardly and in adirection opposite to the direction in which the screw is working and soclear the threads and prevent the clogging thereof, whereby it followsthat the screw may be forced into the work with greater facility andless exertion than would otherwise be the case, the tendency of the woodfibers to return to their normal position assisting in forcing the screwinto position and to hold the same firmer.

To increase the working effect of the screw, I provide the same with acutting lip or point, which may project beyond or below the apex of thecore. In practice a plurality of these cutting-lips are provided and maycorrespond in number with the number of threads carried by the core 8.In the present instance a pair of such cutting lips or points are shown,each spiral thread l0 and 12 terminating in a cutting lip or point l0and 12, respectively, adjacent to the apex of the screw. The outer endsof these spiral thrcads'lO and l2 are shown as coming together near of"just beyond IIO the apex of the core 8 and forming tw'o radial sharpcutting edges or points, somewhat in the nature of wings, disposed inopposition and in angular relation to the axis of the core and adaptedto effectively and quickly cut their way into the wood, whereby thescrew will enter the work with increased facility and with less exertionthan would otherwise be the case. These cutting edges are in the natureof chisel cutting-points, with the cutting edges lower than the heel,and readily lift the wood upwardly and outwardly and quickly form a holeto admit the core of the screw. It will be understood thatin theformation of a single-threaded screw only one of these cutting edges orpoints may be provided. In practice it may be provided with a relativelysharp pitch, which is practicable in this construction of screw, wherebyits speed may be increased. It is preferable in the formation of thisdevice that the threads around the core should be of an open or widepitch, though not necessarily the pitch shown in the drawings, so thatthe threads as they draw the device into the wood will bite the woodfirmly without splitting and at the same time draw the device into thewood at an in'- creased rate of speed.

By constructing the screw in the manner set forth it has been found inpractice that the screw will enter nearly all wood without boring, andin exceptionally hard wood by boring only a slight distance, so that thewood is left in position to hold the screw firmer than otherwise,whereas in the use of the ordinary screw it is necessary irst to bore arelatively deep hole, which displaces and removes the wood, so that whenthe screw is forced into position such wood will not hold the screw withthe same efficiency. Hence its drawing and holding power is to a greatextent destroyed. Moreover, by forming a screw with a pair or aplurality of cutting edges or points the device will cut across orthrough cracks, holes, knots, dac., without altering or changing itscourse.

It will be seen that since in this improved screw the threads arebeveled at their upper sides in a somewhat similar mannervto that inwhich the ordinary threads are beveled at their under sides it followsthat the action of the wood on this improved .device when a drawing oroutward force is exerted thereon will be in a direction opposite to thatin which it is worked-that is to say, the upper inclined or beveledsurface of the screw-threads acts to jam or wedge the wood when anoutward or drawing force is exerted on the screw in a similar manner tothat in which the wood is jammed or wedged by the under faces of theordinary screw when rotated into position, so that the holding power ofthis screw -is superior to the ordinary screw.

This improved screw is of course especially intended for use in wood andis applicable for use in woods of various kinds and degrees of hardness,and is in one form thereof especially adapted for being driven in placeby i means of a hammer, thereby avoiding the slow and tedious operationof inserting the screw by means of the screw-driver. In driv ing a screwof this improved construction in this manner into the wood the extendedspiral relatively flat under surface 14 of the thread forms aresistance-surface, against which the force of the blow is expended, andthis force being distributed over such a relatively extensive area tendsto prevent the driving of the screw downwardly, in view of the angle ofthe thread, with sufficient energy to sever the iibers of the woodimmediately under said resistance-surface and in the line of the edge ofthe thread, while at the same time this action of the under surface inconnection with the relatively steep pitch of the thread tends to rotatethe screw during the driving action with greater speed than it otherwisemight be rotated, and so furnishes the power for operating thecutting-points 10 and 12/ at the Aapex of the screw, whereby thesepoints are made to coperate for boring a hole into which the threadedportion of the screw is forced. It will therefore be observed that thepeculiar cooperation between a screw-thread having the particularconstruction described and the two cuttingpoints is such that thisimproved thread furnishes an effective means for operating saidcutting-points forcutting away the wood to form the small bore, intowhich the somewhat larger core of the screw will be forced bythe blowsto which the screw is subjected while it is being driven into place.

- In the operation of inserting the screw the fibers of the wood asthese are separated by the relatively sharp thread lie, some of them,(those immediately under the thread, as (1,) relatively straight orperpendicmlar to the axis of the screw. Those fibers, as l), however,which naturally come just above the edge of the screw-thread are not cutotf or destroyed, as ordinarily happens with the old kinds of screws,but are turned upwardly, so that the fibers which pass just over theextreme edge are bent at said edge and lie inclined upwardly along thesteep surface'of the thread, as at c. In other words, the lower fibersof the inclined mass of fibers push npwardly the other fibersimmediately above them and also push the fibers outwardly, so as to forma compact mass adjacent to the inclined upper surface l5 of thescrew-thread, thereby constituting a bracing member between saidinclined surface and that region of the wood which lies just outside ofthe screw. Furthermore, this bracing action and the inclination of theupper surface of the thread coperate to prevent the retraction of thescrew by the pressure applied thereto in an outward direction, sincethis inclination of the upper surfaces of the screw-thread, which formto a certain extent a double wedge, owing to its steep inclination bothdownward and sidewise, operates toward IOO IIO

IZO

counteracting the effect which would otherwise be produced by therelatively steep pitch of the screw-thread, which would naturally tendto reduce the security of the fastening.

Owing to the features of construction which I have hereinbefore morefully pointed out the ber of the wood into which the screw isA driven isproperly separated to form the space for the screw-thread, and this witha mini'- mum of destructive action on such fiber, thereby securing asuperior holding power of the screw in the wood, while not retarding theintroduction of the screw by driving instead of by the use of ascrew-driver to turn the screw into place.

In the use of a screw constructed in the manner set forth it has beenfound by actual test that it will penetrate ordinary wood one inch thickin about sixteen (16) turns, while an ordinary screw for the same kindand thickness of wood requires from thirty-eight (38) to forty-two (42)turns underequal power.

I claim as my inventionl. A screw comprised of a core provided with oneor more threads each having a sharp cutting edge located relatively tothe under side of such thread to first engage and upwardly displace thematerial, thereby to decrease the resistance to the entrance of suchthread.

2. A screw comprised of a core provided with one or more threads eachhaving a sharp cutting edge located relatively to the under side of suchthread to iirst engage and upwardly displace the material and therebydecrease the resistance to the entrance of the thread, and each threadterminating in a cutting-lip projecting beyond and at an angle to theaxis of the core.

3. Adevice of the class specified comprised of a core provided with aplurality of threads disposed thereon, each thread having a beveledupper face, a relatively fiat under face, and a sharp c utting edgelocated relatively to the under side of such thread to first engage andupwardly displace the material and thereby decrease the resistance tothe entrance of the thread, and each of said threads terminating in acutting edge or lip projecting beyond and at an angle to the axis ofsaid core;

4. A screw comprised of a core provided with one or more threads locatedthereon and extending beyond the entering end of said core, each forminga radial cutting lip or wing so disposed that its pitch-angle is lessthan the angle between the under surface of the thread and the core.

5. A screw comprised of a core cone-shaped from end to end and providedwith one or more threads each having a sharp cutting edge locatedrelatively to the under side of such thread to rst engage and upwardlydisplace the material and thereby decrease the resistance to theentrance of such thread, each of said threads terminating in a cuttinglip or wing projecting beyond and at an angle to the axis of said core.

G. A screw having a core, cone-shaped from end to end, and a pair ofspiral threads disposed thereon, each of said threads having arelatively flat under face and a beveled upper face and terminating in acutting edge or point adjacent to the end of said core.

7. The herein-described device comprised of a core provided with acone-shaped or beveled end and with a plurality of threads thereon, eachof the threads of such cone-shaped end having a sharp cutting edgelocated relatively to the under side of such thread to first engage andupwardly displace the material and thereby decrease the resistance tothe entrance of the thread, and each of said threads terminating in aradial cutting lip or wing projecting beyond said core.

S. A device having a core provided with a cone-shaped end and two wideor open pitch spiral threads of the same depth throughout and extendingbeyond the apex of the core and forming two radial cutting wings orpoints, each of said threads having a relatively fiat under face and arelatively-inclined

